A074390 a(n) is the least number k that A074389(k) = n.

1, 6, 18, 12, 200, 42, 196, 56, 459, 950, 5203, 396, 9243, 980, 1800, 336, 19363, 270, 13357, 600, 1764, 10406, 72473, 168, 18625, 34814, 4293, 812, 145493, 1350, 15376, 992, 19602, 38726, 41615, 1836, 99937, 26714, 1521, 440, 274003, 3822, 475193

Offset

1,2

Links

Amiram Eldar, Table of n, a(n) for n = 1..1000

Formula

a(n) = Min{x; GCD(x, sigma(x), phi(x)) = n} = Min{x; GCD(x, A000005(x), A000010(x)) = n}.

Example

For n = 79: a(79) = 979837 because GCD(979837,998718,961272) = 79 and 979837 is the smallest.

Mathematica

f[x_] := GCD[DivisorSigma[1, x], EulerPhi[x], x]; t=Table[0, {100}]; Do[s=f[n]; If[s<101&&t[[s]]==0, t[[s]]=n], {n, 1, 1000000}]; t

Prog

(PARI) lista(len) = {my(v = vector(len), c = 0, k = 1, f, i); while(c < len, f = factor(k); i = gcd([k, sigma(k), eulerphi(k)]); if(i <= len && v[i] == 0, c++; v[i] = k); k++); v; } \\ Amiram Eldar, Nov 14 2024

Crossrefs

Cf. A000005, A000010, A073815, A050399, A009195, A009194.

Sequence in context: A097370 A252897 A174904 * A255617 A253771 A223218

Adjacent sequences: A074387 A074388 A074389 * A074391 A074392 A074393

Keyword

nonn

Author

Labos Elemer, Aug 23 2002

Status

approved